Younger potential unrelated hematopoietic stem cell (HSC) donors aged 18-30 are both the most clinically desirable and least available to donate after having preliminarily matched a patient in need of an HSC transplant. The ultimate goal of the proposed investigation is to improve availability of this younger donor group. The proposed study is focused on individuals aged 18-30 and will (a) identify differences between this group and older HSC registry members, (b) identify factors in younger registry members that are associated with opting out of the registry after having preliminarily matched a patient, and (c) generate and evaluate the acceptability and desirability of intervention strategies to improve younger donor availability. Within group comparisons by sex and race/ethnicity and comparison of younger new recruits to a matched sample of older registry members aged 35-44 will provide nuanced information that will allow us to tailor our potential intervention strategies. Our partner for the investigation is the National Marrow Donor Program (NMDP) which manages the largest registry of unrelated HSC donors in the world (> 11 million) and with whom we have an established history of collaboration. This investigation is important because (a) HSC transplantation is now a preferred treatment for life-threatening diseases of the blood, (b) increasing numbers of patients must seek HSCs from unrelated donors, (c) younger donors are the most clinically desirable group of donors, and (d) younger donors have the highest rates of unavailability when asked to donate. Innovative aspects of this research program include that (a) this will be the first systematic investigation focused on better understanding a younger group of potential donors who are both clinically desirable and less available, (b) we include variables such as community engagement, media and technology use, impulsivity, and parental influence which have not been previously included in this type of research but may be increasingly important to donation-related decisions among younger potential donors (c) the differential association of these characteristics with age, sex, race/ethnicity, and donation decisions have not been examined, and (d) this will be the first investigation to lead to the systematic development of intervention strategies to improve availability of younger HSC donors. Study aims are to (a) use web-based surveys to quantitatively describe younger newly recruited donors on five key classes of variables and to examine differences within this cohort by sex and race/ethnicity and between this cohort and an older cohort of newly recruited donors (n=1,248), (b) use web-based surveys to quantitatively compare younger registry members who continue toward donation after matching a patient with those who opt-out of the registry (n=1,440), and (c) to generate and qualitatively evaluate potential intervention strategies to improve younger donor availability. The NMDP strongly supports this investigation and is committed to using study findings to improve recruitment and management strategies for this group of highly valuable younger registry members.